With the advancement of computers, digital holography (DH) has become an important area of interest that has gained much popularity. Research findings derived from this technology enable holograms to be generated with numerical means, wherein the holograms can be displayed using holographic devices, such as a liquid crystal on silicon (LCOS) display. Holograms generated in this manner are in the form of numerical data that can be recorded, transmitted, and processed using digital techniques. On top of that, the availability of high capacity digital storage and wide-band communication technologies also has lead to the emergence of real-time video holography, casting light on the future of 3-D television systems.
At present, development in DH has reached a reasonable degree of maturity, but at the same time, the heavy computation involved also imposes a major bottleneck in practical applications. Although some analytic methods have been proposed recently to overcome the problem, the shortening in the computation time has not been significant. For other methods that are based on a fast central processing unit (CPU) or Graphic Processing Unit (GPU), the hardware involved is complicated, expensive, and requires a substantial power supply.
One part of DH is computer generated holography (CGH), which is a method for digitally generating holographic interference patterns, wherein a holographic image can be generated, for example, by digitally computing a holographic interference pattern and printing it onto a mask or film for subsequent illumination by suitable coherent light source or using a holographic 3-D display (a display which operates on the basis of interference of coherent light) to present the holographic image without the need of having to fabricate a “hardcopy” of the holographic interference pattern each time. One of the major problems in CGH is the high computation cost involved in the calculation of the fringe patterns.
Recently, this particular CGH problem has been addressed by imposing the horizontal parallax only (HPO) constraint whereby the process can be simplified to the computation of one-dimension sub-lines each representing a scan plane of the object scene. Subsequently the sub-lines can be expanded to the two-dimensional (2-D) hologram through multiplication with a reference signal. Furthermore, a hardware solution is available with which sub-lines can be generated in a computationally free manner with high throughput of approximately 100 megapixels per second. Apart from decreasing the computation loading, the sub-lines can be treated as intermediate data, which can be compressed by down-sampling the number of sub-lines.
Despite these desirable features, the method is only suitable for the generation of white light (rainbow) holograms, not Fresnel holograms, and the resolution of the reconstructed image is inferior to the classical Fresnel hologram. Another drawback to such conventional hologram generation is that, if the hologram is illuminated with a monochrome beam, the viewing angle is narrow along the vertical direction. Still another drawback to such conventional hologram generation is that the scan planes are separated by a certain distance so that each holo-line will include an adequate number of rows in the hologram to support the diffraction along the vertical direction. As a result, the resolution of the scene image will be lowered, and further it may be necessary to further decrease the number of scan planes to lower the data rate (if the sub-lines are distributed through certain channels) and computation load, thereby resulting in even more degradation in the visual quality of the reconstructed holographic images.
Today, there is no way of quickly and efficiently generating Fresnel holograms having desirable visual quality and resolution, for example, to enable real-time generation and presentation of Fresnel holograms. Also, today, there is no way of maintaining a desirable viewing angle for the hologram along the vertical direction.
The above-described deficiencies of today's holographic techniques are merely intended to provide an overview of some of the problems of conventional systems, and are not intended to be exhaustive. Other problems with conventional systems and corresponding benefits of the various non-limiting embodiments described herein may become further apparent upon review of the following description.